WASHINGTON — President Barack Obama sternly called on Russian President Vladimir Putin to compel Kremlin-backed separatists to stop hampering the probe at the Ukraine site of a downed passenger jet and allow international investigators unfettered access.

"We have to make sure the truth is out and accountability exists," Obama said Monday from the South Lawn of the White House.

Obama accused the separatists of removing evidence and bodies from the site, actions that he said raise the question of "what exactly are they trying to hide?"

The White House has been seeking to pin responsibility on the separatists for shooting down the Malaysia Airlines plane carrying nearly 300 people. Officials have also pointed a finger at Russia, arguing that it would be all but impossible for the insurgents to operate the sophisticated missile system needed to shoot down a passenger jet without some level of assistance from Russia.